High pressure mercury chromium iodide discharge lamp with phosphor coating

ABSTRACT

A high-efficiency high-intensity blue-emitting discharge lamp combination in which, to the normal arc tube containing a predetermined amount of mercury and the normal outer envelope, there is added a phosphor coating of strontium chloro-apatite activated by divalent europium onto the interior surface of the outer envelope and there is also added chromium and iodine as discharge sustaining additives in the arc tubes. This combination provides a substantially more efficient high-intensity source of blue light than previous sources and is especially useful in the medical and photocopying fields.

United States Patent [191 Larson HIGH PRESSURE MERCURY CHROMIUM IODIDE DISCHARGE LAMP WITH PHOSPHOR COATING [75] Inventor: Daniel A. Larson, Cedar Grove, NJ.

[73] Assignee: Westinghouse Electric Corporation,

' Pittsburgh, Pa.

[22] Filed: Apr. 2, 1973 [21 Appl. No.: 347,082

[52] US. Cl 313/25, 128/395, 313/109, 313/184, 313/229 51 Int. Cl H0lj 61/34, HOlj 61/42- 8 Field of Search 3l3/l09, 25, 184, 229;

[56] I References Cited I UNITED STATES PATENTS 2,748,303 5/1956 Thorington 313/25 3,279,877- 10/1966 Smith et a] 316/16 3,599,028 8/197] Wanmaker et all 313/109 3.658.068 4/1972 McNall 128/395 M 3,821,577 5] June 28, 1974 3,670,194 6/1972 Thornton, Jr. et al 313/109 FOREIGN PATENTS OR APPLICATIONS 1,571,329 6/1969 France Primary EtaminerPalmer C. Demeo Attorney, Agent, or FirmR. A. Stoltz [5 7] ABSTRACT A high-efficiency high-intensity blue-emitting discharge lamp combination in which, to the normal arc tube containing a predetermined amount of mercury I and the normal outer envelope, there is added a phosphor coating of strontium chloro-apatite activated by divalent europium onto the interior surface of the outer envelope and there is also added chromium and iodine as discharge sustaining additives in the arc tubes. This combination provides a substantially more efficient high-intensity source of blue light than previous sources and is especially useful in the medical and photocopying fields.

2 Claims, 1 Drawing Figure CROSS-REFERENCE TO RELATED APPLICATIONS ln copending application, Ser. No. 347,081. filed Apr. 2, 1973, by the present inventor and owned by the present assignee, is disclosed a discharge lamp combination using a titanium iodide additive in addition to the mercury, and also using a phosphor coating of strontium chloro-apatite activated by divalent europium. A high efficient high-intensity source of blue light, especially in the 320-500 nm region is produced.

BACKGROUND OF THE INVENTION This invention relates to high-pressure mercury discharge lamps for uses in which a large amount of blue emission is desired. Such uses include both photocopying and, medical applications.

- Illustrative of the use of a blue-emitting lamp inthe medical field is U.S. Pat. No. 3,658,068 issued to .trum, and a lamp spectral output normalized to the Z-bar spectral tristimulus value (blue-normalized output) provides a measure of the lamps effectiveness for such purposes. Typically such a fluorescent lamp has a blue-normalized output per watt of input power of about 230.

High-pressure mercury vapor lamps using phosphorcoatcd outer envelopes are known in the art. Illustrative is U.S. Pat. No. 3,670,194 issued to Thornton on June I3, 1972 in which one of the components of the phosphor is strontium chloro-apatite activated by divalent europium. Typically such a lamp modified such that strontium chloro-apatite is the only phosphor (rather than part of a blend) has a blue-normalized output per watt of about 100.

High pressure mercury vapor discharge lamps using chrome iodide additives are also known in the art. Such a lamp is described in French Patent No. 1,571,329 issued to L. Georges on June 20, 1969. Such a lamp has a blue-normalized output per watt of about 89.

In the fabrication of iodide additive lamps, the tin iodide has been obtained by adding metallic tin and mercury iodide (from which tin iodide is formed during lamp operation). This is a more convenient method of iodine addition than adding tin iodide during fabrication. Such a process for introducing iodine into an iodide additive lamp is discussed by Smith et al in the 1 U.S. Pat. No. 3,279,877 issued on Oct. 18, 1966.

Thus, high pressure mercury vapor lamps with strontium chloro-apatite phosphors are known in the art,

. neither apparently has been used for medical, photocopying, or other usesrequiring a high blue-normalized output. The low pressure mercury vapor discharge lamps with a strontium halophosphate phosphor activatedwith divalent europium is an efficient source for these purposes, but is a relatively low intensity source.

SUMMARY OF THE INVENTION It has been discovered that a high pressure mercury discharge lamp having a chrome iodide additive and having a strontium chloro-apatite phosphor activated by divalent europium provides high-intensity blue light in a very efficient manner. This high output of blue light is illustrated by the lamps blue-normalized output per watt value of about 154.

The combination includes a discharge lamp having an elongated light-transmitting arc tube enclosing a predetermined volume and containing a predetermined amount of mercury which, when fully vaporized during normal operation of the lamp, will provide predetermined pressure of mercury vapor therein. The combination also has an outer light-transmitting envelope spaced from and enclosing the arc tube. The improvement in the combination comprises a phosphor coating substantially comprising a strontium chloroapatite activated by divalent europium, which is coated on the interior surface of the outer envelope. The improvement also comprises discharge sustaining additives contained in the arc tube, these additives substantially comprising chromium in the amount of about 0.006 to 0.6 milligrams (mg) per cubic centimeter of arc tube volume and iodine in an amount which is at least 70 percent of the stoichiometric amount to form CrI Preferably, the chromium is present in the amount of about 0.17 milligrams per cubic centimeter of arc tube volume, mercury is present in the amount of about 2.5 milligrams per cubic centimeter of arc tube volume and iodine is present in the amount of about 100 percent of the stoichiometric amount to form Crl with said amount of chromium.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of the invention, reference may behad to the exemplary embodiment shown in the accompanying drawing in which:

The sole FIGURE is a side elevational view of a discharge lamp constructed in accordance with the present invention, with parts of the outer envelope and are tube broken away.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the sole FIGURE there is shown the general arrangement of a high pressure mercury vapor discharge lamp within which the. discharge sustaining additives and the phosphor of the present invention are utilized. The lamp, generally designated 10, includes an outer light-transmitting envelope 12 which is sealed to a standard mogul base 14. Mounted within the outer envelope 12 and spaced therefrom is an arc tube 16. The are tube 16 is mounted within the outer envelope 12 by a conventional frame 18 and a pair of straps'20. Sealed within the arc tube 16 disposed at opposite ends thereof are a pair of tungsten operating electrodes 22 and 24. The electrodes 22 and 24 are sealed through the opposite ends of the arc tube 16 by conventional ribbon seals 26. A starting electrode. 28 is also sealed to the arc tube adjacent to electrode 24 by means of a ribbon seal26.

The frame 18 is carried by one of a pair of conventional lead-in conductors 30 which extend through a conventional re-entrant stem press 32 connected to mogul base l4, which in turn is connected to a conventional power source34 in the-well-known manner.

The electrodes 22, 24 and 28 are electrically connected to one or the other of the lead-in conductors 30. A starting resistor 36 is connected between one of the lead-in conductors 30 and the starting electrode 28 through the frame 18.

The discharge materials 38 are contained within the arc tube 16. These discharge materials 38 contain chrmium and iodine as discharge sustaining additives in addition to the conventional mercury. Lesser amounts of other blueemitting discharge sustaining additives (indium iodide, for example) can be included, but chromium iodide as the only discharge sustaining additive is preferred. A phosphor coating 40, substantially comprising strontium chloro-apatite activated by divalent europium is coated on the interior surface of the outer envelope 12.

The lamp configuration is essentially conventional and a more detailed description of its operation may be found in U.S. Pat. No. 2,748,303 issued to Thorington on May 29, 1956.

While the teachings of the present invention are applicable to discharge devices of varying size and designed wattage inputs, a specific example of a lamp constructed in accordance with the present invention is illustrated as a standard 400 watts quartz arc tube 16 having an l8 millimeter inside diameter and about 15 cubic centimeters of internal volume. Such a lamp when charged with a discharge sustaining filling of about 28 milligrams of-mercury, 2.5 milligrams of chromium, and 21 milligrams of mercury iodide and operated at 400 watts (3.4 amps at about 127 volts) will produce, in conjunction with the strontium chloroapatite phosphor activated by divalent europium, approximately 54 lumens per watt (as compared to 48'lumens per watt from a conventional europium activated strontium chloroapatite phosphor coated mercury vapor discharge lamp). When normalized to the Z-bar spectral tristimulus curve (the desired output) the lamp of the instant invention gives an increase of over 50 percent of blue output over the conventional high-pressure mercury strontium chloro-apatite lamp (154 as compared to 100 The divalent-europium activated strontium chloroapatite phosphor used in the lamp of the instant invention is described in copending application Ser. No.

726,464 filed May 3,1968 and owned by the assignee amounts of other blueemitting phosphors (with, for example, a barium-calcium apatite activated with divalent europium), an unmixed strontium chloro-apatite is preferred.

The high pressure mercury lamp with a chromium iodide additive and the high-pressure mercury vapor lamp with a divalent-europium activated strontium chloro-apatite phosphor coating, while providing reasonably high-intensity sources, are comparatively inefficient sources of blue light. When the chromium iodide additive is combined with the high pressure mercury-strontium chloro-apatite lamp, a lamp is produced which is, instead of having a blue output which is a compromise between these two types of high-pressure discharge lamps, has a blue output which is much greater than either one.

The lamp of the instant invention has a much higher intensity output than the strontium chloro-apatite fluorescent lamp. The 400 watt lamp of the instant invention has a blue-normalized output of about 61,500 while a 40-watt fluorescent has a blue-normalized output of only about 9,200. The lamp of the instant invention has the advantage of providing a relatively compact source which can be focused to provide an extremely high-intensity,-and even if multiple fluorescent lamps were used, they could not be focused in a practical manner. Thus, the instant invention provides a most efficient high-intensity source of blue-normalized lumens.

I claim as my invention:

1. In combination with a discharge lamp comprising an elongated light-transmitting arc tube enclosing a predetermined volume and containing a predetermined amount of mercury which when fully vaporized during normal operation of said lamp will provide predetermined pressure of mercury vapor therein, and an outer light-transmitting envelope having an interior surface,

' spaced from and enclosing said arc tube, the improvement which comprises:

a. a phosphor coating substantially comprising strontium chloro-apatite activated by divalent europium on said interior surface of said outer envelope; and

b. discharge sustaining additives contained in said are tube, said additives substantially comprising:

i. chromium in the amount of about 0.006 to 0.6 milligrams per cubic centimeter of said are tube volume; and

ii. iodine in an amount which is at least percent of the stoichiometric amount to form CF12 with said amount of chromium, whereby said combination provides high-intensity blue light having a high Z-bar spectral tristimulus value in a very efficient manner.

2. The combination of claim 1, wherein said chromium is present in the amount of about 0.17 milligrams per cubic centimeter of arctube volume, said mercury is present in the amount of about 2.5 milligrams per cubic centimeter of arc tube volume, and said iodine is present in the amount of about percent of the stoichiometric amount to form Crl with said amount of chromium. 

2. The combination of claim 1, wherein said chromium is present in the amount of about 0.17 milligrams per cubic centimeter of arc tube volume, said mercury is present in the amount of about 2.5 milligrams per cubic centimeter of arc tube volume, and said iodine is present in the amount of about 100 percent of the stoichiometric amount to form CrI2 with said amount of chromium. 